Exhibit Hall | Forum 4
Purpose: The International Atomic Energy Agency will soon publish an updated version of the TRS398 Code of Practice recommending the use of reference-class detectors and consensus k(Q) values for reference dosimetry in megavoltage photon and electron beams. This study evaluates the differences in absorbed dose to water, D(w,Q), determined according to the updated and first versions of TRS398 and the TG51 addendum protocols.
Methods: The procedures required of both versions of TRS398 are identical, indicating the differences in D(w,Q) can be calculated as the ratio of beam quality correction factors, k(Q). The procedure recommended in TG51 addendum differs. Reference dosimetry was performed using NE2571, PTW30013, Exradin A12, IBA CC13 and IBA NACP02 chambers in eight photon and four electron beams. The determined D(w,Q) using both versions of TRS398 and TG51 addendum were compared.
Results: The difference in D(w,Q) for photon beams between both versions of TRS398 ranged from -0.9%–0.2%, with the maximum difference observed at a TPR(20,10) of 0.82 using the NE2571 chamber. For electron beams, D(w,Q) differences ranged from 0.1%–1.7%, with the maximum difference observed at an R(50) of 10.23 g/cm2 using the IBA CC13 chamber. The D(w,Q) differences between the updated TRS398 and TG51 for photon beams ranged from -0.6%–0.3%, with the maximum difference observed at a %dd(10)(x) of 73.52% using a PTW30013 chamber. For electron beams, the differences ranged from 0.5%–1.3%, with the maximum difference observed at an R(50) of 6.72 g/cm2 using the PTW30013 chamber.
Conclusion: The D(w,Q) differences between both versions of TRS398 were within the k(Q) uncertainty published in the first version of TRS398 as 1.0% for photon and 1.7% for electron beams. The D(w,Q) differences between the updated TRS398 and TG51 addendum for electron beams exceed k(Q) uncertainty, stated in the updated TRS398 as 0.6%.
Not Applicable / None Entered.